The present disclosure relates to a phase shifter, an accelerator, and an operating method therefor. The phase shifter comprises a rotating part having a first hollow structure, the first hollow structure having a first cavity, a distance between a circumference of the cross section of the first cavity and a rotation center of the rotating part changing periodically and continuously in a peripheral direction, such that when the rotatory part rotates, a phase shift occurs between two adjacent microwave pulses at an outlet of the phase shifter. The operating method comprises transmitting a microwave pulse within the accelerator at a repetitive frequency v Hertz; the driving devices drives the rotating part to rotate at a rotation speed of n RPM, wherein n=15v*m, m is an odd number, 1, 3, 5 . . . , such that when transmitting a microwave pulse each time, the long axis of the oval cross section of the first cavity of the rotatory part is rotated to a horizontal or vertical state.